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Message from discussion turn list of letters into an array of integers

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More options Oct 24 2012, 8:04 am
Newsgroups: comp.lang.python
Date: Wed, 24 Oct 2012 05:03:52 -0700 (PDT)
Local: Wed, Oct 24 2012 8:03 am
Subject: Re: turn list of letters into an array of integers
Chris Rebert於 2012年10月24日星期三UTC+8下午2時07分29秒寫道：

> On Tue, Oct 23, 2012 at 10:23 PM, seektime <michael.j.kra...@gmail.com> wrote:

> > Here's some example code. The input is a list which is a "matrix" of letters:

> >    a  b  a

> >    b  b  a

> > and I'd like to turn this into a Python array:

> You mean a Python list. The datatype Python calls an `array` is very

> different and relatively uncommonly used.

> Although, confusingly, Python's lists are implemented using C arrays

The list in python is a list of valid python objects.
For the number crunching part, please use  arrays in numarray and scipy.

> >   1 2 1

> >   2 2 1

> > so 1 replaces a, and 2 replaces b. Here's the code I have so far:

> >>>> L=['a b a\n','b b a\n']

> <snip>

> >>>> seq

> > '1 2 1\n 2 2 1\n'

> > My question is how can I turn "seq" into a python array?

> I'd say you're asking the wrong question. The better question is "Why

> wasn't the result a list in the first place?". Many transformations

> are cumbersome to express over just strings, which is why the first

> job of most programs is to parse their input into a more convenient

> structure that is suited to their main task(s).

> This (along with some other improvements) leads to a better, somewhat

> different program/algorithm:

> letter2number = {'a': 1, 'b': 2}

> with open("path/to/file.txt", "r") as f:

>     result = [[letter2number[letter] for letter in

> line.strip().split()] for line in f]

> If it's safe to assume that the correspondence between the letters and

> numbers isn't completely arbitrary, some further improvements are also

> possible.

> Some relevant docs:

> Cheers,

> Chris

> P.S.: I'm guessing you obtained `L` from file.readlines() or similar;

> it is worth noting for future reference that the readlines() method is

> considered somewhat deprecated.

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